In numerous applications of devices in the medical field, a tubular structure having a sealed lumen along its length may be a necessary or desirable component of the device. It is often useful for the sealed tubular structure to have a variety of characteristics in order to be adaptable for different applications. At times, it is also important for the sealed tubular structure to have different characteristics and construction along the length of the tubular structure. Different characteristics of the tubular structure may be provided by including multiple layers of material that overlap with each other and form the tube wall.
Some medical devices incorporate a tubular structure in the form of a catheter having an internal lumen for transporting material, fluid, and/or suction pressure between the ends of the catheter. The catheter walls effectively seal the lumen to prevent liquid or gasses, including air, from contacting certain device elements, entering the body through the device, seeping in such as where suction pressure may be diluted, or leaking out of the device such as where suction pressure may be lost.
Intracorporeal medical devices having catheters are employed for therapeutic and/or diagnostic procedures. Different types of catheters have different levels of flexibility to enable the catheter to deliver material to and remove material from an internal body site. Guide catheters are placed in a patient to guide another device to a target internal body site. Operating catheters are used to deliver a device, such as a stent, an angioplasty device, an atherectomy or thrombectomy device, or the like, to the target internal body site.
In some particular applications of a catheter, atherectomy or thrombectomy devices are used for treatment of arterial occlusions. Atherosclerosis is a condition arising from the deposition of fat-like matter, i.e. plaque, on the walls of blood vessels. As a result of accumulated obstructions, blood flow becomes restricted or blocked, creating health risks, including coronary artery disease, angina and heart attacks. Most methods of using atherectomy and thrombectomy devices involve placement of a guiding catheter into the body and insertion of a guidewire, over which an operating head is guided to a target site where an occlusion is located within a blood vessel. However, devices that do not employ guidewires are also possible. The catheter surrounds a drive shaft to effectively isolate the rotating elements of the device from direct contact with any healthy body matter, e.g. tissue. The drive shaft is coupled to an operating head that is advanced, and in some devices, rotated to cut or ablate the obstruction and to restore or improve blood flow in the vessel.
Regardless of the particular application for the tubular structure, problems which must be overcome to establish a sealed tubular structure are particularly difficult when at least portions of the tube is required to be highly flexible. Flexibility of sections of a catheter is of specific concern where an intracorporeal medical device must be routed along a tortuous path, such as through blood vessels and various internal structures, before placement at the target site. An obstructed blood vessel, for instance, may be located in peripheral vessels, coronary vessels, cranial vessels, or other areas. For example, where the target site is in a femoral vessel, such as in a groin region, the catheter may be introduced into one leg, e.g. a retrograde stick, and guided in an upward direction, around a sharp angle in the torso and down again towards the opposite leg having the injury. In this particular case, the catheter should have at least a highly flexible end and middle portion to negotiate the sharp curvature in the path. However, the catheter must also include some stiffness to permit the catheter to be pushed into the body. Thus, not only should the layers of the tubular structure be sealed, but also permit varying levels of flexibility along at least portions of the tubular structure.
A further concern of a tubular structure is that the structure may kink where the structure must be formed around a sharp curve or bend. Infusion or withdrawal of liquids through the lumen of the tubular structure may be required during operation of a device. In this case, the tubular structure must have sufficient stiffness to resist collapse or enlarge of the lumen under a range of pressures and force conditions. For example, a wall of a catheter that caves in due to flexing may significantly block the lumen space and decrease transport within the lumen. Thus, it is essential that tubular structures used in connection with such devices be as flexible as possible during placement and removal, yet have a high degree of structural integrity for operation of the device.
Some previous attempts at designing a kink-resistive tubular structure provided a layer of a coiled, braided or otherwise weaved member that has tight loops and that is fixedly attached to or embedded in a polymeric layer, such as a polyimide or plastic layer. Although the construction of the layer may allow for a small amount of flexibility, the use of a weaved or coiled layer attached to or embedded in a polymeric layer generally results in a tubular structure that is stiffer in portions of the structure than which is required by many applications. Some tubular structure designs that include such layers are described in U.S. Pat. Nos. 6,464,684; 6,197,014; and 5,868,767.
Another challenge in forming a layered tubular structure is in creating close and reliable contact between multiple flexible layers, such that one layer encases another layer and is permanently affixed to at least a portion of the other layer. One current construction of a tubular structure having multiple layers includes a layer of thermally shrinkable material overlapped with an inner layer. Heat is applied to melt and shrink the thermally shrinkable layer into contact with the inner layer. In this manner, the thermally shrinkable layer molds to the underlying layer, but does not necessarily bond to the underlying layer.
Thus, although conventional thermally shrinkable material forms closely overlapped layers, the layer may not be sufficiently bonded to create a sealed tubular structure in a manner that is durable and reliable and can be used under a variety of pressure and force requirements. For example, fluoropolymer plastics, such as polytetrafluoroethylene (PTFE), e.g. TEFLON material (from i.e. Dupont DeNemours Corp., in Wilmington, Del.) are sometimes included in the thermally shrinkable layer to reduce friction as the tubular structure is guided through the body. Unfortunately, the lubricity of fluoropolymers makes it generally difficult to bond the fluoropolymer to other layers by using conventional methods and adhesives.
Some efforts to bond fluoropolymer layers that are not thermally shrinkable include etching the surface of the fluoropolymer to change the surface characteristics and make the layer “sticky”. Although etching has generally been useful for bonding non-thermally shrinkable material that includes fluoropolymer plastics, the etching technique has not typically been applied to the surface of thermally shrinkable material for bonding. In general, the process of heating thermally shrinkable material is thought to melt the etchings on the material surface to such as great extent that the etchings are rendered useless for bonding.
The present invention is directed to improved tubular structures in which thermally shrinkable materials are closely associated with other layer(s) to provide a sealed tubular structure that is flexible, kink-resistant, and has a high degree of structural integrity. The present invention fulfills these needs and provides further related advantages.